1. Field of the Invention
The invention relates to cathode ray beam deflection systems and more particularly to beam deflection amplifier systems employed in electromagnetic deflection systems.
2. Description of the Prior Art
One prior art deflection amplifier system of interest with respect to the present invention is disclosed in the J. M. Spencer U.S. Pat. No. 3,816,792 for a "Cathode Ray Tube High Speed Electromagnetic Deflection System", issued June 11, 1974, and assigned to Sperry Corporation. Spencer describes a deflection system including a differential input amplifier stage and a push-pull current controlling output stage which drives the deflection coil of the display system. A sampling resistor is connected in series with the beam deflection coil to provide a negative feed back voltage proportional to coil current for use in promoting linear operation of the system. One terminal of a capacitor is connected to the end of the beam deflection coil coupled to the input amplifier output terminal, while the other terminal of the capacitor is connected through a bidirectional switch to a potential source. The bidirectional switch consists of a transistor and a diode connected in parallel, each constituting a respective half of the switch and operative in respective halves of the cycle of resonant oscillation which occurs during the resonant retrace interval. When the deflection amplifier system is operating in the linear mode, the bidirectional switch is non-conducting and, therefore, the capacitor is effectively disconnected from the deflection coil. In the non-linear mode, the bidirectional switch functions to connect the capacitor conductively with the beam deflection coil; simultaneously, a second switch effectively disconnects, the coil-capacitor circuit from the input amplifier, whereby resonant current flow occurs between the beam deflection coil and the capacitor to effect the desired rapid, energy saving retrace. Other prior art of interest is discussed in the H. C. Hilburn U.S. Pat. No. 3,786,303 for a "Cathode Ray Tube Dual Mode Horizontal Deflection Control Amplifier", issued Jan. 15, 1974 and also assigned to Sperry Corporation. These prior art configurations, though they accomplish their objectives in an entirely satisfactory manner, have a common limiting defect, in that the fly-back capacitor shunts the deflection coil. This fact limits the operating band width of the circuit, increases the level of power dissipation, and increases the chances of unstable operation. While the arrangement of U.S. Pat. No. 3,816,792 did advantageously switch the fly-back capacitor out of the circuit cyclically, complexity and parts count were undesirably increased. Of course, the shunting effect of the capacitor was not fully removed.